TARGAS-1 Operation Manual V. 1.02 157 support@ppsystems.com
Soil Respiration Measurements
The TARGAS-1 software assumes a quadratic relationship (y = a + bx + cx
2
) between the chamber
concentration (C=y) and time (T=x) from the start of measurement to account for the non-linearities
caused by leakage. Note that there is a delay after the chamber is first placed on the soil to allow for the
establishment of stable gradients before the measurements begin.
(2.2) The quadratic equation is
= + +
Where and are a series of chamber CO
2
concentration measurements made over time, and , ,
are coefficients calculated from a least square fit of the data.
The respiration rate will be calculated from the rate of change of CO
2
at time zero or / at =0.
(2.3) Differentiating equation (1.2) yields
= +
(2.4) And evaluated at T = 0,
=
A comparison of and gives an indication of the magnitude of the non-linearity of the C vs T data. The
TARGAS-1 software indicates a "non-linear" error message whenever the value is greater than 20% of
. This is believed to be a better approach than lowering the CO
2
value at the start of the measurement.
In addition to the quadratic assumption and calculation, the TARGAS-1 software also calculated the
respiration (or assimilation) using a linear assumption.
(2.5) The linear equation is
= +
(2.6) which evaluates again to
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